T?:yr)Excy of species to form varieties. 21 



any conspicuous magnitude, because it would make itself felt at the very- 

 first step, bv rendering existence difficult and extinction almost sure soon 

 to follow. An origin such as is here advocated will also agree with the 

 peculiar character of the modifications of form and structure which 

 obtain in organized beings — the many lines of divergence from a central 

 type, the increasing efficiency and power of a particular organ through 

 a succession of allied species, and the remarkable persistence of unim- 

 portant parts such as colour, texture of plumage and hair, form of horns 

 or crests, through a series of species differing considerably in more es- 

 sential characters. It also furnishes us with a reason for that 'more 

 specialized structure' which Professor Owen states to be a characteristic 

 of recent compared with extinct forms, and which would evidently be 

 the result of the progressive modification of any organ applied to a 

 special purpose in the animal economy. 



We believe we have now shown that there is a tendency in nature 

 to the continued progression of certain classes of varieties further and 

 further from the original type — a progression to which there appears 

 no reason to assign any definite limits — and that the same principle 

 which produces this result in a state of nature will also explain why 

 domestic varieties have a tendency to revert to the original type. This 

 progression, by minute steps, in various directions, but always checked 

 and balanced by the necessary conditions, subject to which alone ex- 

 istence can be preserved, may, it is believed, be followed out so as to 

 agree with all the phenomena presented by organized beings, their ex- 

 tinction and succession in past ages, and all the extraordinary modifi- 

 cations of form, instinct, and habits which they exhibit. 



Ternate, February, 1858. 



VOL. LX.- 



